Revert "- persuade social to at least compile"

This reverts commit 4938775bf405d8720ae5adce20bd5d66492e75a2.

git-svn-id: https://gnunet.org/svn/gnunet@34019 140774ce-b5e7-0310-ab8b-a85725594a96
Revert "- convince gcc to compile"

This reverts commit cd2a54791e6286c3c437b525b26f6e9268956afc.

git-svn-id: https://gnunet.org/svn/gnunet@34020 140774ce-b5e7-0310-ab8b-a85725594a96
social: implement enter/leave/messaging; psyc: improvements and fixes

- social: implement enter/leave, send/receive messages, slicer
- psyc, social: add struct GNUNET_PSYC_Message for single-fragment join messages
- psyc: add message callback in addition to message part callback
- client_manager, social, psyc, multicast: add disconnect callback

git-svn-id: https://gnunet.org/svn/gnunet@34021 140774ce-b5e7-0310-ab8b-a85725594a96